An organic optoelectronic device is, for example, an organic light emitting diode (“OLED”) display, an OLED light source used for general purpose lighting, an organic light sensor array, an organic solar cell array, or an organic laser. The OLED display can be, for example, a passive matrix display, an alpha-numeric OLED display, or an active matrix OLED display. In the specific case of the OLED display, the display is typically comprised of an anode layer and a cathode layer where the anode layer is typically patterned to form multiple anode strips and cathode layer is patterned to form multiple cathode strips. The anode strips intersect the cathode strips, and pixels are formed at the intersections of the anode strips and the cathode strips by sandwiching one or more organic layers between the anode strips and the cathode strips.
The organic optoelectronic device requires protection from reactive gasses such as oxygen and moisture in the atmosphere, and therefore employ some form of encapsulation. One common procedure to encapsulate the organic electronic device is to sandwich it between a substrate and an encapsulation lid, and a continuous adhesive layer around the perimeter of the device bonds together the substrate and the encapsulation lid such that the device is sealed. The adhesive layer is typically not impermeable to oxygen and particularly not to moisture, so the encapsulated device package will generally have some finite permeation rate. These reactive gases that permeate through the adhesive layer react with the cathode layer and prevent electron injection at the sites of reaction. The reactive gasses that permeate through the adhesive seal react with the cathode layer at, for example, pinholes in the cathode layer or at the edges of the cathode strips. Eventually, the sites of reaction reach some specified quantity, and the device is considered no longer useable.
For a fixed permeation rate into the encapsulated device package, employing getters inside the package can extend the useable lifetime of the device. These getters absorb some portion of the reactive gases that would otherwise react with the cathode layer. When getters are employed, the overall package can be visualized as two scavenging systems operating in parallel, one being the cathode layer and the other being the getter. While getters absorb some portion of the reactive gasses that permeate through the adhesive seal, a significant portion of the reactive gasses still reach the cathode layer of the OLED display thus prematurely making the device no longer usable prior to the getter reaching its capacity limit.
The academic solution to the permeation problem is to use an extremely fast getter or employ a completely impermeable hermetic seal—a true barrier for the cathode layer. These solutions, although desirable, are not easily attainable or easily implementable given current techniques and materials. The deposition of a thin-film barrier layer without pinholes cannot be easily achieved. Even for the case of a fast getter, there can be complications implementing it in a manufacturing environment. Also, the device's design specification may require a relatively slow getter (this requirement may be due in part to getter availability or cost), thus an extremely fast getter may not be available.
An aluminum capping layer is typically deposited onto the cathode strips for protection; however, the capping layer only protects the top of the cathode strips, but not the edges of the strips. The reactive gasses can attack the edges of the cathode strips causing detrimental effects such as pixel shrinkage. The pixel shrinkage occurs when the reactive gasses that permeate through the adhesive layer react with the edges of the cathode strips and the areas that react with the gasses no longer inject electrons resulting in no emission of light from these areas.
For the foregoing reasons, there exists a need to encapsulate the organic optoelectronic device that is easily implementable, and is effective at increasing device lifetime by, for example, protecting the edges of the cathode layer and increasing the proportion of reactive gasses absorbed by the getter.